The overall objective of the proposed study is to elucidate physiochemical properties of various dietary fibers prior to further consideration of their possible use in human clinical trials in cancer prevention. Specifically, we propose to study the effect of intact fibers, namely wheat bran and oat bran, and of isolated fiber fractions, namely cellulose and pectin, on (1) fecal bulk and fatty acids, (2) metabolic activity of gut microflora using fecal bacterial Beta-glucuronidase and 7Alpha-dehydroxylase activities, (3) fecal bile acids and mutagens, and (4) Ca, Mg, Zn and Cu in blood plasma. About 90-100 healthy subjects consuming a high-fat/low-fiber American diet will be screened for fecal mutagenic activity. Healthy subjects (n=28) who have shown to have significant level of fecal mutagenic activity from the above screening, will be selected for diet intervention study and will serve as their own controls throughout the study. After 4 weeks of baseline diet data collection, the participants will be asked to follow the prescribed (supplemental) dietary fiber level for 6 weeks, after which normal baseline diet without supplemental fiber will again be resumed for 4 weeks. This pattern will be followed for each of the 4 dietary fibers. Fecal and blood specimens will be collected from each individual 2 times during each baseline diet period and 2 times during supplemental dietary fiber period for each fiber under study. Fecal and blood samples will be analyzed for the above biochemical parameters. The data will be analyzed statistically to determine the effect of various dietary fibers on the biochemical parameters. These studies will provide the needed information on the effect of various dietary fibers on fecal constituents that seemingly play a role in colon carcinogenesis.